I haven't seen many viruses/malware that run once. To be on the safe side, however, upload the file to Virus Total at https://www.virustotal.com/ on the web and see what about 60 AVs say about it. I like to see at least 2 of these AVs detect something before I believe it: Avira, Bitdefender, Eset Nod 32, Kaspersky, and Sophos.

An advantage of scanning a file on Virus Total is that if it is a false positive (erroneous detection), Virus Total will notify the detecting AV so they can fix it. In our case, ClamWin uses the scan engine and virus signatures of Clam AV, and it might take Clam AV a while to get around to fixing it--a consequence of a free AV that only has people working on it in their spare time.